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Патент USA US2046061

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‘2,046,061
Patented June 30, - 1936
UNITED STATES PATENT OFFICE
2,046,061
COATED METAL
Leo P. Curtin, Cranbury, and James M. Payne,
Carteret, N. J., assignors to Curtin-Howe Cor
poration, New York, N. Y., a corporation of
New York
No Drawing. Application January 10, 1935,
Serial No. 1,258
17 Claims.
This invention relates to coated metals; and it
comprises an article of steel or iron carrying a
thin black surface layer containing vanadium in
combination with oxalic acid, said layer being
hard, permanent, elastic enough to resist flex
‘ ing to a marked degree and serving as a bonding
agent between the metal and subsequently ap
plied paint, cohering to both; and it further
comprises a method of coating ferrous metal and
10 preparing it for painting wherein the cleaned or
pickled ferrous metal is exposed to the action of a
solution containing tetravalent vanadium and
oxalic acid and is thereafter washed and dried;
all as more fully hereinafter set forth and as
15 claimed.
In the metal ?nishing industry, it is now cus
tomary prior to painting to apply some type of a
protecting coating to the clean metal; this pre
,
(Cl. 148-65)
oping at 10 per cent of the rate at which the
bright metal alone would rust. The coating is
therefore a rust retardant.
We have found that coatings satisfactory as a
protective agent for iron and steel and as a bond- 5
ing agent linking paint to iron or steel can be
made with a solution containing vanadium oxa
lates; and that these coatings exhibit a further
advantage in that they offer a considerable re
sistance to rupture by ?exing. Sheet metal so 10
coated can be bent at a very sharp angle with
no tendency for the coating to crumble, even at
the inner edge of the bend. The coating im
proves the resistance of the sheet metal to sharp,
heavy impact and is fairly resistant to high tem
peratures, even up to 300° C.
In contradistinc
tion to the usual types of coating, this may be
described as rust-proo?ng; it is not merely rust
liminary coating serving as a basis for subsequent
painting, varnishing and enameling. For the
most part, it is difficult to secure completely pro
retarding.
tective coatings with ordinary types of paints and
?rmly cohering coating is formed and, after
washing and drying, the underlying bright metal
is wholly protected. The solution is made by dis
varnishes applied directly to clean naked iron or
steel. One type of preliminary coating often used
is that produced by the action of solutions of
By immersing clean pickled sheet metal in an 20
acidi?ed solution of a vanadium oxalate, a dark,
solving vanadium tetroxid with the aid of oxalic
phosphoric acid or of acid phosphates, on iron.
It contains ferrous phosphate and often other
phosphates as well. A solution containing a
acid and the same chemicals are used in replen
ishment. A slight amount of oxalic acid in excess
is employed but it is not necessary to have free
manganous phosphate is sometimes used.
acid present in greater amount than suffices to
prevent hydrolysis of the vanadium oxalate. A 30
pH ranging from 1 to 3 serves well. The coating
bath should be rather hot, somewhere between
50° C. and 99° C. The time of treatment varies
When
30 such a phosphate coating is washed and dried,
it serves as a good basis for varnish, paint and
lacquer. These coating materials cohere or bond
better to the phosphated surface than they do to
the naked metal. Besides phosphoric acid, other
acids have been used as coating agents, the coat
ings consisting of metallic salts of the respective
acids used.
A difficulty with most of these coatings of the
prior art is that they do not resist ?exing well; if
40 coated sheet metal is bent at a sharp angle, there
is a tendency to open flaws and crevices. Coat
ings satisfactory in most other respects are apt
to be de?cient in this; the coated metal often will
not stand the manipulation necessary in making
45 up various things; automobile bodies, for exam
ple. With a rupture in the coatings due to ?ex
from 4 to 5 minutes to several hours.
With 4 or
5 minutes treatment, the bath ordinarily gives ex
tremely thin black coatings; but the thickness is
su?icient for some purposes.
5
A- heavier type of
coating is obtained with immersion for several
hours. The color of the coating varies from a
rich lustrous black to a dull black. It may be
made decorative, in event no after-painting is
used. With a rich lustrous black in the coating
and a layer of transparent varnish, decorative
effects are obtained.
In making a typical coating bath in the present
0
coatings, while customarily called “rustproof”,
invention, 166 parts of commercial vanadium
tetroxid, V204, are dissolved in 10,000 parts of
water with the aid of 260 parts of commercial
oxalic acid. This bath contains the equivalent
of 1.66 parts V204 to 100 parts of water, but higher
are actually more in the nature of rust re
and lower concentrations can be used.
tardants.
coatings can be produced with V204 concentra
tions ranging from 0.3 to 4.0 per cent. A bath s0
prepared may be used inde?nitely long with oc
casional replenishment of the contained vana 55
ing, there is the possibility of what is called
“creeping corrosion”; rust appears under the
double coatings and spreads inde?nitely. These
In damp locations, with any frac
ture or abrasion of the coating which exposes
bright metal, rusting of the whole surface ulti
55 matelv occurs; the rust, however, perhaps devel
Good
2 r
’
2,046,961
dim and oxalic acid. The'vanadyl oxalate may
be used in the corresponding amount. Commer
ciaii vanadium pentoxid, V205, may be used in re
plenishing the bath; it being reduced by oxalic
acid to the vanadyl form. Additions of oxalic
acid should be in the amounts required to keep
the bath clear. Should a sludgeaof insoluble
ferrous oxaiate or of insoluble ‘reduced vanadium
compounds form it can be cleared up by cautious
additions or? strong commercial hydrogen peroxid
solution in the right amount; Ferrous oxalate is
converted into ferric oxalate. Weak solutions
give an undesirable dilution and it is not ad
vantageous to add enough 'peroxid to cause sub
15 stantial oxidation in the bath itself. Bubbling
air through the bath is sometimes expedient.
An addition of V205 can sometimes be utilized
in producing the limited amount ofoxidation
wanted. The precise nature of the solute con
20 tained in the bathimade as described ante is not
known and it changes after use in coating ferrous
metal. Reduction‘ appears to take place; triva
lent vanadium appearing. Ferrous oxalate is
special purposesgdesirable to heat it. Heating
may be up to a low red heat, of even by direct
impingement of a ?ame. The color changes from
black to dark blue. Undoubtedly, the oxalate
radical breaks up. The bluish coating left after
heating, however, has substantiaiiy the same de
sirable physical and chemical properties, as well
as the rust resistance, 'as an unheated similar
coating.
1
The coating bath in the present invention is 10,
acid, having a pH between 1 and 3. Alkaline
baths do not give the same results; a vanadium
containing, rust resisting coating’on ferrous met
al. In an acid solutiomthe vanadium is present
as a cation and a coating is formed containing 15
vanadium without production of iron hydroxids;
without rusting the metal.
1
As stated, the presence of iron compounds in
the vanadium coating bath is often advantageous.
Conversely, it is found that small additions of 20
vanadium compounds improve the action of other
oxalate coating baths. Iron is commercially
coated by treatment with a solution of ferric
also present. Ferrous oxalate although insoluble i,oxalate and a small addition of a vanadium com
arpound to this bath improves the results; it gives a
25 in water and in oxalic acid solutions, has a rather
substantial solubility in a solution of vanadium
oxalates. In the use of the bath with iron and
steel, ferrous oxalate can be formed and go into
solution. The presence of this ferrous oxalate in
30 soiution is apparently desirable, up to concen
trations of about, say, 0.5 per cent ferrous oxalate
in the bath.
In forming the coating the iron metal is at
tacked and there is a production of ferrous
35 oxalate, some of which becomes part of the coat
ing. Some goes into the bath. In the coating,
there are trivalent and tetravalent vanadium;
there are derivatives of vanadium trioxidf'VzOs.
Vanadium'forms a number of different oxids and
40 they combine among themselves, so that it is
possible that intermediate oxids between the
trivalent and tetravalent are present, these'being
in'combination, probably, with theioxalyl radical,
although "vanadites of vanadium" or of ferrous
45 iron may be present. In some instances the coat
ing appears to contain a basic oxalate which may
be a vanadyl oxaiate corresponding to the for
mula V204.VO C294.
As stated, the ‘path always contains more or
50 less iron and this iron is useful in forming and
contributing the coatings. It has been found
that good ' coatings may be ‘obtained with baths
in which the amount of iron present is greater
than that incident to the formation and solution
55 of ferrous oxalate. Small additions of ferrous
oxalate are sometimes useful in bringing the bath
to its steady state. Sometimes ferric oxalate is
' added.
Good coatings can be made with a bath
containing about equal proportions of vanadyl
80 oxalate and ferric oxalate; say about 1.5 per cent
or‘ each.
'
The composition of the coating layer in all
cases is complex but whatever its composition, it
has the describedadvantageous properties. Its
65 resistance to rusting is about fouftimes as great
as that of similar commercial “rustproofed” metal
produced by prior processes. In comparative
tests of the prior material and the present mate
rial, with plates or “panels” each carrying three
70 coats of lacquer, they were sharply scratched to
expose bright metal and’ comparative observa
tions made at weekly intervals showed about 4
fold resistance in the present material.
As stated ante, the coating is resistant to heat;
75 and, as a matter of fact, it is sometimes, for
better coating. .The coating is darker and its
rust resisting properties are considerably improved. Iron can be coated in a solution of oxalic
acid alone although its action isprather slow and
an addition of a small amount of vanadium 30
oxalate improves the results.
While we have particularly described the use
of oxalic acid in making the bath, other organic
acids may be used, but, as we at present think,
Solutions made with citric
and tartaric acids give coatings which, made
‘ with less advantage.
under the conditions described, are not as good
as those made with oxalic acid. Phosphoric acid
used as a substitute for oxalic acid in the direc
tions given ante, produces a coating better than
is given by tartaric orcitric acid under the same
conditions. Good coatings can be made by these
other acids, but their properties are somewhat
different from those of the coating made with
oxalic acid.
In all cases, the bath should be acid to the do;
scribedtextent, with a pH between 1 and 3. re
preserving the desired acidity an addition of acid
sodium oxalate is useful as a buffer salt.
What we claim is:- ,
50
1. As a new manufacture, a ferrous metal ob
ject having formed thereon a rustproo?ng co
herent surface coating containing oxalates and
vanadium.
2. The method of rustproo?ng ferrous metals
which comprises immersing such metal in a‘
55
slightly acid solution containing vanadium as an
oxalate.
.
3. The process of ‘claim 2 wherein the slightly
acid solutionI has a pH between 1 and 3.
4. The process of claim 2 wherein.’ immer
sion is at a temperature between 50°- and 99° C.
5. In the rustproo?ng of sheet metal, the process
which comprises immersing a plurality of succes
sive sheets in a replenished bath containing a 65
vanadium oxalate, replenishment being by addi
tions of oxalic acid and V204 and the tendency
of both to deposit insoiuble products being cor
rected by occasional oxidative treatments.
6. In the process of claim 5, as an oxidative 70
treatment, bubbling air through the ‘solution.
'7. In the precess of claim 5, as an oxidative
treatment, an occasional introduction of V205.
8.-In the process of claim 5, introducing hy
drogen peroxid as an oxidative treatment.
75
,
2,046,061
3
9. In rustproo?ng ferrous metal articles and
providing a protective coating, the process which
coherent surface coating of a vanadium com
comprises immersing such an article in a re
pound, said coating being impervious and being
plenished bath containing vanadium and iron as
oxalates with enough excess oxalic acid to keep
the solution clear, withdrawing, washing and
resistant to rupture by ?exing or impact.
14. The article of claim 13 wherein the coat
ing containing vanadium has the characteristics
of a baked vanadyl oxalate coating.
15. An article having a surface of ferrous metal
having formed thereon a. protective coherent
drying.
10. In the process of claim 9, the method of
replenishment which comprises occasional addi
10 tions of V204, of oxalic acid in the amount nec
essary to keep the solution slightly acid and of
an iron oxalate.
11. As a rustproo?ng method for ferrous metal,
the process which comprises forming upon a fer
15 rous metal article a coherent surface coating con
taining oxalates and vanadium and afterwards
heating the article to break up the oxalyl radical.
12. The process of providing ferrous metal ob
jects with a rustproo?ng coating whichmomprises
20 immersing such an object in a slightly acid solu
tion of a vanadium salt, the acidity having a
pH value of ,1 to 3.
13. As a new manufacture, a ferrous metal ob
ject having formed thereon a thin, black, hard,
oxalate coating containing a substantial amount 10
of vanadium in addition to other metallic oxalates.
_ 16. An article having a surface of ferrous metal
having formed thereon a coherent protective
coating containing a vanadium oxalate in addi
tion to iron oxalate.
17. A process of providing ferrous metal ob
jects with a rustproo?ng coating which com
prises exposing such an object to the action of
an acidulated solution containing a vanadyl salt
of an acid of the group consisting of oxalic, citric, 20
tartaric and phosphoric acid.
LEO P. CURTIN.
JAIWES M. PAYNE.
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